Many simple compounds of elements such as AlCl3,GaCl3 and InCl3 are covalent while anhydrous but in aqueous solution, these are ionic in nature. In anhydrous condition, the (charge\/radius) ratio, i.e. polarisability of Al3+ is high and hence, according to Fajans' rule, Al3+ polarises Cl− ions to large extent, there introducing covalent character in the compound, i.e. AlCl3 behaves as a covalent compound in anhydrous conditions. In aqueous medium the ions get hydrated, because the amount of hydration enthalpy released exceeds, the sum total of ionisation enthalpy required. Since, the (charge\/radius ratio of hydrated aluminium ion is much smaller as compared to that of Al3+, the tendency of [Al(H2O)6]3+ topolarise hydrated Cl⊖ ion decreases and the resulting hydrated compound is ionic in nature.